The present invention relates to a vehicle state estimating apparatus, a suspension control apparatus and a suspension system for use in a vibration control of a vehicle.
For example, in a suspension control apparatus and a suspension system for use in a vibration control of a vehicle, an observer may be used for estimation of a motion state of the vehicle. Generally, such estimation of a motion state of a vehicle by an observer requires creation of a linear approximation model of the vehicle. In particular, the linear approximation model should have detectability, and an estimated control force input into the vehicle approximation model should be the same as an actual control force input into an actual vehicle. Unsatisfaction with these conditions may result in reduced estimation accuracy or impossibility of estimation.
However, if a suspension control apparatus and a suspension system employ a control suspension which generates variable control force, such as a semiactive damper or an active suspension, it is difficult to estimate a same control force as an actual control force due to the nonlinearity of such a suspension.
As a solution to this problem, there is an apparatus disclosed in Japanese Patent Application Public Disclosure 2001-287528. The apparatus disclosed in Japanese Patent Application Public Disclosure 2001-287528 is characterized in that the nonlinearity of control force of a control suspension [for example, a damping force generated by a semiactive damper and a force generated by an active suspension (a force called an active force, in contrast to a damping force corresponding to a resistance force)] is understood in advance by carrying out experiments, a map for calculating an estimated control force or an approximation function is created based on the experimental data, an estimated control force as close to an actual control force as possible is calculated with use of the map or the function as a control force estimating means, and then a motion state of a vehicle is estimated. In the apparatus disclosed in Japanese Patent Application Public Disclosure 2001-287528, the control force estimating means is a static system.
However, a control suspension is not a static system but a dynamic system. Therefore, time lag occurs relative to an actual control force in the apparatus disclosed in Japanese Patent Application Public Disclosure 2001-287528 since its control force estimating means is a static system. Because time lag occurs in this way, the difference expands between an estimated control force and an actual control force accordingly, as a result of which accuracy of estimating a motion state of the vehicle is reduced and it becomes difficult to provide a desired control effect.
To provide an excellent control effect, accuracy of estimating a motion state of a vehicle should be improved. To improve this accuracy, an actual control force should be estimated in consideration of not only the nonlinearity but also the dynamic characteristic (time lag) of a control suspension.